Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 186	$ 196
Maximum Amount of Future Payments under Credit Default Swaps	$ 9,216	$ 9,609
Weighted Average Years to Maturity	4 years 6 months	4 years 9 months 18 days
Credit Risk Derivative Assets, at Fair Value	$ 186	$ 196
Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	29	32
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,948	$ 1,987
Weighted Average Years to Maturity	2 years 1 month 6 days	2 years 6 months
Aaa/Aa/A | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 5
Maximum Amount of Future Payments under Credit Default Swaps	$ 169	$ 208
Weighted Average Years to Maturity	3 years 6 months	2 years 8 months 12 days
Aaa/Aa/A | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 24	$ 27
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,779	$ 1,779
Weighted Average Years to Maturity	2 years	2 years 6 months
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 157	$ 159
Maximum Amount of Future Payments under Credit Default Swaps	$ 7,166	$ 7,567
Weighted Average Years to Maturity	5 years 1 month 6 days	5 years 4 months 24 days
Baa [Member] | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 2	$ 3
Maximum Amount of Future Payments under Credit Default Swaps	$ 139	$ 249
Weighted Average Years to Maturity	2 years 7 months 6 days	2 years 6 months
Baa [Member] | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 155	$ 156
Maximum Amount of Future Payments under Credit Default Swaps	$ 7,027	$ 7,318
Weighted Average Years to Maturity	5 years 1 month 6 days	5 years 6 months
B
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 5
Maximum Amount of Future Payments under Credit Default Swaps	$ 55	$ 55
Weighted Average Years to Maturity	4 years 6 months	5 years
B | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 5
Maximum Amount of Future Payments under Credit Default Swaps	$ 55	$ 55
Weighted Average Years to Maturity	4 years 6 months	5 years
Ba
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (1)	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 32	$ 0
Weighted Average Years to Maturity	4 years 6 months	0 years
Ba | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 0	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 12	$ 0
Weighted Average Years to Maturity	4 years 6 months	0 years
Ba | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (1)	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 20	$ 0
Weighted Average Years to Maturity	4 years 6 months	0 years
Caa3
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (4)	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 15	$ 0
Weighted Average Years to Maturity	4 years 6 months	0 years
Caa3 | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (4)	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 15	$ 0
Weighted Average Years to Maturity	4 years 6 months	0 years